Integrated light emitting device, integrated sensor device, and manufacturing method

ABSTRACT

The present disclosure relates to an integrated light emitting device. The integrated light emitting device comprises a substrate of semiconductor material, a light emitting unit integrated into the semiconductor material, and at least one cavity formed into the semiconductor material between the substrate and the light emitting unit. At least portions of the at least one cavity may be formed by Silicon-On-Nothing (SON) process steps.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/196,203, filed Jun. 29, 2016, which claims the benefit of GermanPatent Application No. 10 2015 110 496.2 filed Jun. 30, 2015, which areincorporated by reference as if fully set forth.

FIELD

Embodiments generally relate to semiconductor devices and methods formanufacturing semiconductor devices, and, more particularly, tointegrated light emitting devices and related integrated sensor devices

BACKGROUND

Electronic sensors generally measure a physical quantity and convert themeasured physical quantity into a signal that is provided to anelectronic instrument (e.g., integrated chip processor). In recentyears, the number of areas using sensors has vastly expanded. Forexample, sensors can be found in diverse applications such as chemicalagent detection units, medical diagnostic equipment, industrial processcontrols, pollution monitoring, automobiles, etc.

Infrared sensors such as for instance mid-infrared (MIR) sensors measureradiation emitted in the infrared (IR) portion of the electro-magneticspectrum from objects having a temperature above absolute zero. Themid-infrared spectrum covers electromagnetic radiation with wavelengthsin a range of approximately 2-25 μm. By measuring changes in the MIRspectrum, sensors are able to measure changes in a sample's chemistry ortemperature, for example.

The reduction of the optical path length (millimeter andcentimeter-range today) is one central tasks on the way tomonolithically integrated IR sensors. One promising approach is theapplication of evanescent surface fields in waveguides of sub-wavelengthdiameters. To take full advantage of this concept, an efficientcollimation and coupling of infrared light into a fiber as well as anexcellent thermal isolation of a light emitter is desired.

SUMMARY

An embodiment of the present disclosure relates to a semiconductor-basedintegrated light emitting device. The device comprises a substratecomprising a semiconductor material, i.e., a semiconductor substrate.The integrated device further comprises a light emitting unit integratedinto the semiconductor material, and at least one cavity formed into thesemiconductor material between the substrate and the light emittingunit.

In particular, at least parts of the cavity may be formed below portionsof the light emitting unit and above portions of the semiconductorsubstrate. Commonly, such a cavity is referred to as Silicon-On-Nothing(SON) cavity.

In some embodiments, the light emitting unit comprises, as light source,an electrically conductive structure formed in the semiconductormaterial. The electrically conductive structure is configured to emitlight when a supply voltage is applied to terminals of the electricallyconductive structure.

In some embodiments, the electrically conductive structure comprisescrystalline, polycrystalline or amorphous semiconductor material.

In some embodiments, the electrically conductive structure comprises anelectrically conductive filament extending perpendicular to a directionof a light beam emitted from the light emitting unit.

In some embodiments, the light emitting unit further comprises a beamshaping portion which is configured to collimate light emitted from theelectrically conductive structure. The beam shaping portion may comprisea light-reflecting rounded or parabolic edge of the light emittingunit's semiconductor material.

In some embodiments, the electrically conductive structure substantiallyextends through a focus of the rounded or parabolic edge.

In some embodiments, the light emitting unit further comprises a filterportion formed in the semiconductor material. The filter portion may beconfigured to have at least one pass band in the spectral infraredregion.

In some embodiments, the filter portion comprises one or more trenchesformed into the light emitting unit's semiconductor material.

In some embodiments, the light emitting unit is arranged in a portion ofthe semiconductor material sealed off an environment. The light emittingunit in the sealed portion may be at least partially surrounded by anevacuated cavity.

In some embodiments, the integrated light emitting device furthercomprises a sealing layer formed above the light emitting unit and atleast one cavity between the light emitting unit and the sealing layer.

In some embodiments, the integrated light emitting device furthercomprises a waveguide coupled to a light outlet of the light emittingunit. The waveguide may be configured to provide interaction betweenguided light and a measurement medium surrounding the waveguide.

In some embodiments, the waveguide and the light emitting unit areintegrally formed into the semiconductor material.

In some embodiments, the waveguide is arranged in a portion of thesemiconductor material open to an environment. The light emitting unitmay be arranged in a portion of the semiconductor material sealed offthe environment.

In some embodiments, a width of the waveguide is smaller than theemitted light's wavelength. Optionally, a height of the waveguide may belarger than the light's wavelength.

According to a further aspect of the present disclosure it is providedan integrated sensor device. The integrated sensor device comprises asemiconductor substrate, a light emitting unit formed into thesemiconductor substrate, a light detecting unit formed into thesemiconductor substrate, and a waveguide formed into the semiconductorsubstrate between the light emitting unit and the light detecting unit.The waveguide is formed in a portion of the semiconductor substrate opento an environment to provide interaction between guided light and ameasurement medium surrounding the waveguide. The light emitting unit isformed in a portion of the semiconductor substrate sealed off theenvironment. Further, the light emitting unit in the sealed portion isat least partially surrounded by an evacuated cavity.

In particular, at least parts of the evacuated cavity may be formedbelow portions of the light emitting unit and above portions of thesemiconductor substrate. Commonly, such a cavity is referred to aSilicon-On-Nothing (SON) cavity.

According to a further aspect of the present disclosure it is provided amethod for forming an integrated light emitting device. The methodincludes integrating a light emitting unit into a semiconductor materialof a semiconductor substrate and forming at least one cavity into thesemiconductor material between the semiconductor substrate and the lightemitting unit. Note that the at least one cavity may actually be formedinto the semiconductor material before the light emitting unit iscreated.

In some embodiments, forming the at least one cavity comprises forming acavity below the light emitting unit by using a Silicon-On-Nothing (SON)processing sequence.

In some embodiments, integrating the light emitting unit comprisesintegrally forming, with the light emitting unit, a waveguide into thesemiconductor material.

In some embodiments, integrating the light emitting unit comprisesforming an electrically conductive filament structure into theintegrating the light emitting unit.

In some embodiments, integrating the light emitting unit comprisesforming a filter structure having one or more trenches into thesemiconductor material.

In some embodiments, integrating the light emitting unit comprisesforming a light-reflecting curved or parabolic edge into the lightemitting unit's semiconductor material, the curved or parabolic edgeacting as beam shaping element.

Embodiments may combine an integrated light emitter, a collimation unitand a spectral filter on a single semiconductor element. This elementmay be thermally isolated from surrounding material by evacuatedcavities. Thereby efficient collimation and coupling of infrared (IR)light into an optical sub-wavelength fiber as well as an excellentthermal isolation of the emitter may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of apparatuses and/or methods will be described in thefollowing by way of example only, and with reference to the accompanyingfigures, in which:

FIG. 1a illustrates a carbon dioxide concentration in a ventilated roomas a function of time, with a ventilation rate as a parameter;

FIG. 1b illustrates a carbon dioxide concentration in an upper class carwith stopped ventilation as a function of time, with a number ofoccupants as a parameter;

FIG. 1c shows a schematic diagram of a linear non-dispersive gas sensorwith an optical path length in the range of centimeters;

FIG. 2 illustrates a semiconductor-based integrated light emittingdevice according to one or more embodiments;

FIG. 3 shows a perspective view of a light emitting unit for IR spectralsensors according to one or more embodiments;

FIG. 4 shows a simulated transmission spectrum for a silicon/vacuumlayer stack as illustrated in FIG. 3;

FIG. 5 illustrates a high-level flowchart of a method for manufacturinga semiconductor-based integrated light emitting device according to oneor more embodiments;

FIGS. 6a-6c show various principles of forming Silicon-On-Nothing (SON)cavities;

FIG. 7 illustrates a final structure of a semiconductor-based integratedlight emitting device after sealing and evacuation; and

FIG. 8 shows a flowchart of a method for manufacturing thesemiconductor-based integrated light emitting device of FIG. 7.

DETAILED DESCRIPTION

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare illustrated. In the figures, the thicknesses of lines, layers and/orregions may be exaggerated for clarity.

Accordingly, while further embodiments are capable of variousmodifications and alternative forms, some example embodiments thereofare shown by way of example in the figures and will herein be describedin detail. It should be understood, however, that there is no intent tolimit example embodiments to the particular forms disclosed, but on thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of thedisclosure. Like numbers refer to like or similar elements throughoutthe description of the figures.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of furtherexample embodiments. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises,” “comprising,” “includes” and/or “including,” whenused herein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art, unlessexpressly defined otherwise herein.

A constantly increasing amount of publications and concepts deals withdetection and characterization of chemicals in gases and other fluids.The progressive miniaturization of components of these measurementsystems paves the way for opening up new markets. One example is themeasurement of carbon dioxide (CO₂) concentrations in closedenvironments. The American Society of Heating, Refrigerating, andAir-Conditioning Engineers (ASHRAE) provided some insight into the roleof demand controlled ventilation for buildings.

FIG. 1a and FIG. 1b illustrate the concentration of CO₂ in cars andbuildings as a function of time (ventilation rate, number of occupantsas parameters). FIG. 1a shows an example CO₂ concentration in aventilated room as a function of time, with ventilation rate as aparameter. FIG. 1b depicts an example CO₂ concentration in an upperclass car with stopped ventilation as a function of time, with a numberof occupants as a parameter.

Acceptable CO₂ levels are in the range of 600 ppm (parts per million),complaints of stiffness and odors occur at 600 to 1000 ppm, generaldrowsiness is associated with 1000-2500 ppm. For the example of CO₂concentration in cars, ventilation becomes a matter of safety. On theother hand, fuel efficiency is one of the driving factors in carautomation. A reduction of fuel consumption at a level of up to 0.9l/100 km have been estimated when a sensor-controlled ventilation bydemand is used instead of conventional ventilation setups.

Heating at residential and public buildings is one major contributingfactor of CO₂ emission in countries in temperate zones. In Germany, forexample, the associated consumption of energy is currently roughly 7000kWh per person and annum. This correlates to a CO₂ emission ofapproximately 3.5 tons (assuming oil or natural gasoline as predominantenergy sources). Although heating of buildings is only a third of theoverall energy consumption in Germany, the CO₂ emission for heating ofbuildings is already well above the level of 2 tons per person and annumthat is acceptable concerning global warming. The reduction of effortsfor heating of buildings is intimately connected with a gas-tightconstruction and demand controlled ventilation as a basis for efficientheat insulation.

The above illustrated facts show the need of sensor-controlled airquality management, for example. Two sensor approaches may be regardedas promising candidates for widespread usage in buildings:Non-dispersive infrared (NDIR) sensing systems and photo-acousticsensors. Although both systems show sufficient resolution and keyparameters, some major disadvantages are still unsolved—first of allsensor dimensions and costs.

A broad range of sensing principles for fluid or gas detection has beeninvestigated in the past decades. For example, infrared spectroscopy maybe performed using radiation in the infrared region of theelectromagnetic spectrum (i.e., radiation having wavelengths ofapproximately 2-25 μm). Many modern days sensors, such as non-dispersiveinfrared (NDIR) CO₂ sensors, for example, use the infrared region of theelectromagnetic spectrum to measure properties of fluid and/or gassamples. Such sensors generate IR radiation, which when brought intocontact with the samples, reacts with the samples to cause a change(e.g., attenuation) in the IR radiation.

FIG. 1c shows a schematic diagram of a conventional linearnon-dispersive sensor 100. Sensor 100 includes a broadband infraredlight source 102, a sample chamber 103, one or more light filters 108,and an infrared detector 110. The sample chamber 103 may comprise aninlet 104 and an outlet 106 for the sample, e.g., gas or fluid. Sensor100 is non-dispersive in the sense of optical dispersion since infraredenergy is allowed to pass through the atmospheric sample chamber 103without deformation. Here, the optical path length of the conventionalsensor 100 may be in the range of centimeters.

Sensor 100 measures changes in the IR radiation spectrum to determineproperties of a sample in sample chamber 103. The measurement ofcharacteristic absorption of the sample in the IR radiation spectrum,which represents a chemical fingerprint as particular substances, showstronger absorption at certain wavelengths being characteristic for thesubstance. This feature can be used by exposing the substance tobroadband IR radiation and determining the absorption in the spectrumafter the radiation has passed through or partly penetrated the sample.

One of the target research topics for NDIR sensors has been theoptimization and reduction of optical path lengths needed for CO₂detection in the 100 ppm range. Some investigations yielded singlecomponents of NDIR sensors as integrated parts of a silicon chip.Principally, all components have been demonstrated separately as silicondies. However, the full advantage of silicon physical propertiesconcerning infrared wave guiding and spectral filtering is rarelyexploited in more than one component.

The reduction of the optical path length (millimeter andcentimeter-range today) is one central task on the way to monolithicallyintegrated (gas) sensors. One promising approach is the application ofevanescent surface fields in waveguides of sub-wavelength diameters. Totake full advantage of this concept, an efficient collimation andcoupling of infrared light into the sub-wavelength fiber as well as anexcellent thermal isolation of the light emitter is essential.Embodiments of the present disclosure address this issue.

Turning now to FIG. 2, it is illustrated a schematic cross-sectionalview of an integrated semiconductor light emitting device 200 accordingto one or more embodiments.

The integrated light emitting device 200 comprises a semiconductorsubstrate 205, such as a semiconductor wafer, for example. In variousembodiments the semiconductor substrate 205 may be doped with an n-typeor p-type dopant concentration or may not be doped. In otherembodiments, the semiconductor substrate 205 may comprise an epitaxiallayer. The semiconductor substrate 205 is made of semiconductormaterial, such as Silicon (Si) or Germanium (Ge), for example. Note thatin principle also other semiconductor materials are possible as long asthey provide a band gap between the valence band and the conduction bandadequate for guiding light through the semiconductor material. Theintegrated light emitting device 200 further comprises a light emittingunit 210 integrated into the substrate's 205 semiconductor material. Inother words, the light emitting unit 210 is formed or structured fromand into semiconductor material of the semiconductor substrate 205. Thatis, the light emitting unit 210 and the substrate 205 may be formedmonolithically. Various embodiments of the integrated light emittingdevice 200 are characterized in that at least one cavity 215 is formedinto the semiconductor material between the substrate 205 and the lightemitting unit 210. The cavity 215 separates the semiconductor basedlight emitting unit 210 from the remaining semiconductor substrate 205,thereby providing for thermal isolation between the light emitting unit210 and the semiconductor substrate 205. For optimum thermal isolationthe cavity 215 may be evacuated. The light emitting unit 210 above loweror bottom portions of the cavity 215 may be provided in a so-calledSilicon-On-Nothing (SON) sheet layer. Consequently, the part of thecavity 215 below the light emitting unit 210 may be a SON cavity.

As illustrated in FIG. 2, the semiconductor body of the light emittingunit 210 may comprise an electrically conductive filament structure 212as light source—similar to the filament of a bulb. Other light sourceimplementations, such as electrically conductive plates orLight-Emitting Diodes (LEDs), for example, are also conceivable.However, forming the filament structure may be synergistically combinedwith forming other similar structures in the semiconductor device 200,such as trenches for optical filters, transistors or capacitors, forexample. The electrically conductive filament structure 212 may beformed in the semiconductor body of the light emitting unit 210, forexample, by using conventional deep trench etching processingtechnology. A structure with appropriate extension of a few microns totens of microns may be etched in the light emitting unit's 210semiconductor body and then be filled with electrically conductivematerial to obtain the conductive filament. Some examples of appropriateelectrically conductive material for the filament 212 include tungsten,polycrystalline, crystalline, or amorphous semiconductor material. Someembodiments use a portion of the SON silicon layer as the emittingelement. In this case, a trench structure is surrounding the saidportion, leaving out only small fixtures between the emitting unit andthe surrounding material.

In the example of FIG. 2, the electrically conductive filament structure212 extends vertically from an upper surface 214 of the light emittingunit's 210 semiconductor body to a lower surface 216 of the lightemitting unit's semiconductor body. That is, electrically conductivefilament structure 212 extends perpendicular to a direction of lightemitted from the light emitting unit 210. Respective electric supplyterminals (not shown) may be provided to the upper and lower ends of theelectrically conductive filament structure 212. In this way, theelectrically conductive filament structure 212 may be configured toradiate (IR−) light when an adequate supply voltage of below 1V to 20Vis applied to the supply terminals.

Note that the at least one cavity 215 extends between the lower surface216 of the light emitting unit 210 and an upper surface 218 of thesemiconductor substrate 205. The lower surface 216 and the upper surface218 face each other. The at least one cavity 215 provides thermalisolation between the light emitting unit 210 and the semiconductorsubstrate 205. As indicated in FIG. 2, the isolating cavity 215 maysubstantially surround the whole semiconductor body of the lightemitting unit 210 to thermally isolate the light emitting unit 210 fromthe remaining semiconductor substrate 205 from which the light emittingunit 210 has been formed. That is to say, the cavity 215 may not onlylaterally separate the semiconductor body of the light emitting unit 210and the substrate 205, but also vertically.

In order to mount or fix the light emitting unit 210 in the cavity 215,the integrated light emitting device 200 may comprise one or moresupport or fixation structures 240 deposited between the substrate 205and the light emitting unit 210. The support or fixation structures 240are configured to mount the light emitting unit 210 in the cavity 215.Here, the support structures 240 are configured as webs. In someembodiments, the one or more support structures 240 may comprise aninsulating material, for example, an oxide of the semiconductormaterial, such as, for example, silicon dioxide (SiO₂). Note that theSiO₂ fixation 240 has a much smaller thermal conductivity compared tothe Si of light emitting unit 210. Thermal isolation between lightemitting unit 210 and substrate can hence be maintained. In this contextthe skilled person will appreciate that the support or fixationstructures 240 should be dimensioned possibly small for possiblymaximizing thermal isolation. The support structures 240 may be obtainedby selective structuring/oxidization of the semiconductor substrate 205,for example.

As indicated by FIG. 2, the integrated light emitting device 200 mayfurther comprise an optional waveguide 220 coupled to a light outlet 222of the light emitting unit 210. The waveguide 220 may be configured toprovide an interaction between light emitted from the light emittingunit 210 and guided by the waveguide 220 and a measurement medium (e.g.gas, fluid) surrounding the waveguide 220. The conveyed light forms anevanescent field that extends outward from the waveguide 220 to interactwith a sample, e.g. a gas or a fluid, positioned in portions of theevanescent field. As the evanescent field interacts with the measurementmedium the radiation guided by the waveguide 220 is attenuated accordingto one or more characteristics of the measurement medium (e.g., inparticular, the radiation is absorbed in a wavelength regioncorresponding to the wavelength of the guided wave or waves). Anoptional light or radiation detector 260 may then be configured toreceive the attenuated IR radiation and to determine the one or morecharacteristics of the sample from the attenuated IR radiation. Theradiation detector 260 may include a ComplementaryMetal-Oxide-Semiconductor (CMOS) based infrared photodetector, forexample. In some embodiments, the optional radiation detector 260 maycomprise a radiation detector integrated into the semiconductorsubstrate 205, while in other embodiments the radiation detector 260 maycomprise an external radiation detector.

Some embodiments make use of evanescent surface fields and a phenomenoncalled “frustrated total (internal) reflection”. Total internalreflection occurs at the boundary of two dielectric media, e.g., betweenwaveguide 220 and measurement medium surrounding the waveguide 220, if alight wave propagates from an optically denser medium refractive indexn₁ into one of lower density refractive index n₂, and the angle ofincidence exceeds the critical angle, given by arcsin(n₂/n₁). However,even if the angle of incidence is larger than the critical angle, theelectric field penetrates into the adjacent medium in the form of anevanescent wave. The penetration depth is in the order of a wavelength,and can be measured by “frustrating” the reflection by adding anoptically dense third medium at a distance on the order of a wavelengthfrom the first medium, in which case the evanescent wave is coupled tothe third medium and carries energy. The coupling strength falls offnearly exponentially as the distance between the first and third mediais increased.

In the example embodiment of FIG. 2, the waveguide 220 and the lightemitting unit 210 are integrally or monolithically formed into thesemiconductor material. That is to say, both a body of the lightemitting unit 210 and the waveguide 220 may be formed out of one pieceof the same semiconductor material provided by the semiconductorsubstrate 205. Hence, the waveguide 220 may be a silicon waveguide insome embodiments. This allows for particularly well light emission andguidance, minimizing losses. The waveguide 220 may also be embedded in acavity 215′. At least parts of cavity 215′ may be formed by SON processtechnology. The cavity 215′ may provide for thermal isolation betweenthe waveguide 220 and the semiconductor substrate 205 as well as ameasurement chamber for interaction between guided light and ameasurement medium surrounding the waveguide 220. The skilled personhaving benefit from the present disclosure will appreciate that aseparate arrangement of light emitting unit 210 and waveguide is alsowell possible.

Optionally, the light emitting unit 210 may also comprise a filterportion 230 formed in the semiconductor body of the light emitting unit210. The filter portion 230 may be positioned between the broadbandinfrared light source 212 and the light emitting unit's light outlet 222to filter the broadband infrared spectrum radiated by light source 212in a manner that provides for a narrowband infrared radiation that is tobe conveyed by the waveguide 220. In some embodiments, the filterportion 230 comprises one or more substantially parallel trenches 232vertically extending into the light emitting unit's 210 semiconductormaterial. Other optical filter implementation, such as photoniccrystals, for example, are also conceivable. However, forming thetrenches may be synergistically combined with forming other structuresin the semiconductor device 200, such as transistors or capacitors, forexample. The widths of the respective trenches may be adapted to providea pass band of the filter portion 230 in the spectral infrared region.The person having benefit from the present disclosure will appreciatethat the same trench etching process steps may be used to form one ormore vertical holes for the electrically conductive filament structure212 and the trenches 232 of the filter portion 230.

A perspective view of an example semiconductor component 300 of anintegrated light emitting device is shown in FIG. 3. Note that theillustration of FIG. 3 does neither show any semiconductor substrate norany cavities between the semiconductor substrate and the semiconductorcomponent 300.

The illustrated semiconductor component 300 comprises a light emittingportion 310 and a waveguide portion 320. The light emitting portion 310and the waveguide portion 320 are integrally formed from thesemiconductor material of a SON sheet layer, i.e., a semiconductor layercovering a SON cavity. That is to say, in the shown example the lightemitting portion 310 and the waveguide portion 320 constitute a singlepiece of semiconductor material. An IR signal may thus be directlycoupled from the light emitting portion 310 to the waveguide portion320. It may be advantageous to use sub-wavelength dimensions for width wand/or height h of the wave guide 320. For an example wavelength of 4.3μm the width w may be about 2 μm, for example. As mentioned earlier,this may reduce the absorption length needed by several orders ofmagnitude. In the illustrated example, a vertical height h of thewaveguide portion 320 is larger than a lateral width w of the waveguideportion 320. This may be beneficial for manufacturing purposes. For thementioned effect of “frustrated total (internal) reflection” w and/or hshould be smaller than the light's wavelength. A doping in the waveguide320 should not be too large. In some examples, the concentration of n-or p-type dopants should be smaller than 10¹⁵/cm³

Since a lateral width of the light emitting portion 310 is larger thanthe lateral width w of the waveguide portion 320, a transition 322 fromthe light emitting portion 310 to the waveguide portion 320 is formedtrumpet-like in the embodiment of FIG. 3. Note, however, that othergeometries of light emitting portion 310 and the waveguide portion 320are also possible.

As has already been explained with reference to FIG. 2, the lightemitting portion 310 of FIG. 3 comprises a broadband IR light source 312and a filter structure 330 formed into the semiconductor materialbetween the light source 312 and the waveguide portion 320. The filterstructure 330 comprises a plurality of trenches 332 formed into thesemiconductor material of the light emitting portion 310. The pluralityof trenches 332 may be evacuated, respectively. Also, different trenches332-1, 332-2 may have different respective thicknesses b₁, b₂. Therespective dimensions of the different trenches is relevant for thepass-band of the optical filter structure 330. An example for aninfrared filter stack has been calculated using silicon and vacuum foralternated optical layers. The thicknesses of single layers are well inthe ballpark of processing capabilities of state-of-the-art deep trenchetching. The simulated transmission spectrum for a silicon/vacuum layerstack as illustrated in FIG. 3 is shown in FIG. 4.

As can be seen from FIG. 4, providing the filter structure 330 with astack silicon/vacuum layers with the respective illustrated thicknessesleads to a narrow pass band around an IR wavelength of approximately 4.3μm.

Turning back to FIG. 3, the light emitting portion 310 further comprisesa beam shaping portion 350 at the end opposing the waveguide portion320. The beam shaping portion 350 is configured to collimate lightradiated from the light source 312. In the shown example, the beamshaping portion 350 comprises a light-reflecting curved or parabolicedge of the light emitting unit's semiconductor material. Preferably,the light source 312, e.g. the electrically conductive filament,substantially extends through a focus of the rounded or parabolic edge.Here, the electrically conductive filament 312 substantially correspondsto a focal line extending from a top surface 314 to a bottom surface ofthe parabolic beam shaping portion 350. The skilled person willappreciate that also lens structures could be implemented as opticalcollimator. Also in this case the light source would be positioned inthe focus of the lens.

As schematically shown by FIG. 5, embodiments also provide a method 500for forming the integrated light emitting device 200.

Method 500 includes integrating 510 the light emitting portion 210, 310into the semiconductor material of the semiconductor substrate 205, andforming 520 the at least one cavity 215 into the semiconductor materialbetween the semiconductor substrate 205 and the light emitting portion210, 310. As will be appreciated by the skilled person having benefitfrom the present disclosure, integrating 510 the light emitting portion210, 310 and forming 520 the at least one cavity 215 are closelyinterrelated. The light emitting portion 210, 310 is formed into thesemiconductor substrate 205 by forming 520 the at least one cavity 215below and/or beside and/or above the light emitting portion 210, 310,and vice versa. That is to say, an order of acts 510 and 520 may also bereversed.

Some embodiments use a so-called Silicon-On-Nothing (SON) processingsequence to form the at least one cavity 215 and/or to provide furtherbasic structural elements of integrated light emitting device 200. Inother words, the at least one cavity 215 between the substrate 205 andthe light emitting unit 210 may be provided by applying a SON processingsequence, an example of which will be explained in more detail below.

After forming a SON sheet layer, in which light emitting portion 210,310 and waveguide portion 220, 320 may be structured later, a deeptrench etch may define filament 212, 312, transmission filter 230, 330and emitting/absorption portions. Intermediate oxidation processes maytransform silicon fixations 240 between substrate 205 and light emittingunit 210, 310 to a silicon oxide layer. In this way, the thermal powerconduction between emitter and substrate 205 may be minimized.

Beside the use of sacrificial layers below the SON sheet layer for thefabrication of a silicon on nothing (SON) structure, a further practicalmethod for obtaining SON structures with a desired size and shape mayuse the so-called Empty-Space-in-Silicon (ESS) formation technique. Ithas been shown that a SON structure can be precisely controlled by theinitial shape and layout of trenches. The size of ESS is determined bythe size of the initial trench(es). The desired shapes of ESS, such asspherical, pipe-shaped and plate-shaped, can be fabricated by changingthe arrangement of the initial trenches. Some examples of SON processingmake use of the self-organizing recrystallization caused by siliconsurface migration. The initial trench shape patterned on the siliconsubstrate may be regarded as the most important factor to fabricate aSON structure. The trench structure transforms so as to minimize thesurface energy, when it is annealed in a deoxidizing ambient, such ashydrogen.

Trench transformation by surface migration results in theEmpty-Space-in-Silicon (ESS). The SON structure can be made of SON sheetlayer over ESS by this means. Typical examples of ESS formation, whoseshapes are spherical, pipe-shaped and plate-shaped, are schematicallyillustrated in FIG. 6.

An isolated deep trench 601 may be transformed to a spherical ESS 602,see FIG. 6 a. Formation of the spherical ESS begins at the top andbottom corners of the deep trench, because the radius of curvature ofthese regions is the smallest. This result indicates that the diameterof the spherical ESS becomes larger than that of the initial trench.Thus, trenches 603 closely arranged in a row are transformed to thepipe-shaped ESS 604, due to the combination of the grown spherical ESSat the bottom of each trench, see FIG. 6 b. A plate-shaped ESS 606 canalso be fabricated by developing this technique. By arranging thetrenches in a lattice 605, the spherical ESSs at the bottom of alltrenches are combined, and they are transformed to a large, thinplate-shaped ESS 606, see FIG. 6 c.

Turning now to FIG. 7, it is illustrated a schematic perspective view ofan integrated semiconductor light emitting device 700 according to oneor more further embodiments. For the sake of brevity a detaileddescription of like or similar elements that have been described beforewill be omitted.

The integrated semiconductor device 700 comprises a semiconductorsubstrate 705. In a SON sheet layer 707 above the semiconductorsubstrate 705 the integrated semiconductor device 700 comprises a lightemitting unit 310 integrally formed with a waveguide 320 in the SONsheet layer 707. Light emitting unit 310 and waveguide 320 have beenexplained in detail with reference to FIG. 3. Above the SON sheet layer707 the integrated semiconductor device 700 also comprises a sealinglayer 709. The sealing layer 709 may comprise various sealing materials,such as thermoplastic, elastomeric or metallic materials, for example.Here, silicon oxide, silicon nitride or polysilicon layers areappropriate candidates as well. SiO₂ fixations 740 and 740′ fix lightemitting unit 310 and waveguide 320 in between the semiconductorsubstrate 705 and the sealing layer 709. At the same time the fixations740 and 740′ seal the light emitting unit 310 off a measurementenvironment. In other words, the light emitting unit 310 is arranged ina portion of the semiconductor device 700 sealed off an outerenvironment. Boundaries or sidewalls of the sealed portion are formed bythe substrate 705 (bottom), the sealing layer 709 (top), and the SiO₂fixations 740 and 740′. The light emitting unit 310 in the sealedportion is surrounded by or embedded in an evacuated cavity 715 forthermal isolation. As can be seen from the illustrative example of FIG.7, the light emitting unit 310 may be surrounded by the evacuated cavity715 from below, above, left, before, and behind the light emitting unit310. Only the right side of light emitting unit 310 with the sidewaysoptical signal outlet may be supported by the SiO₂ fixations 740 and740′and adjoin the measurement environment. At least the cavity portionbelow the light emitting unit 310 may be formed by SON processing. Theskilled person will appreciate that other geometries may also be wellsuited for sufficient thermal isolation between semiconductor substrate705 and light emitting unit 310.

The semiconductor based waveguide 320 extends from the light emittingunit 310 in the sealed portion 710 to a portion 720 of the semiconductordevice 700 which is open to the measurement environment. This openportion 720 may also be referred to as absorption portion or unit. Thewaveguide 320 extending through the open absorption portion 720 isconfigured to provide interaction between guided light and a measurementmedium, e.g., a gas or a liquid, surrounding the waveguide 320 in theabsorption portion. For example, in order to provide inlets and/oroutlets the sealing layer 709 may be at least partially open above thewaveguide 320 in the absorption portion 720. A length of the waveguide320, i.e., the optical path length, may be in the range of 10 μm toseveral 100 μm.

An embodiment of integrated semiconductor device 700 may be manufacturedby using the example method 800 illustrated in FIG. 8. It will beappreciated that while method 800 is illustrated and described below asa series of acts or events, the illustrated ordering of such acts orevents are not to be interpreted in a limiting sense. For example, someacts may occur in different orders and/or concurrently with other actsor events apart from those illustrated and/or described herein. Inaddition, not all illustrated acts may be required to implement one ormore aspects or embodiments of the disclosure herein. Also, one or moreof the acts depicted herein may be carried out in one or more separateacts and/or phases.

Method 800 starts with the provision and appropriate doping 810 of a Siwafer. For example, certain regions of the later light emitting unit 310may be doped. In a further act 820 the SON-cavities 715, 715′ may beprocessed. This may include etching of sacrificial layers and/or ESSformation as explained above, for example. In a subsequent act 830 thelight emitting and waveguide portions 310, 320 above the SON-cavities715, 715′ may be formed in the semiconductor substrate by further deeptrench etching acts. To obtain the portions of the cavities 715, 715′above the light emitting and waveguide portions 310, 320 one or morefurther sacrificial layers may be deposited and structured above the SONsheet layer 707 in an act 840. During this act the upper SiO₂ fixation740′ may be obtained. After that, in an act 850, sealing layer 709 maybe deposited and structured above the SON sheet layer 707. In a furtheract 860, sacrificial layers may be removed by selective etching.Finally, metallization layers may be structured for electrical routingand/or contacts, see 870.

When combining the integrated light emitting devices 200, 700 with alight sensor or detector integrated on the same semiconductor substrate,an integrated sensor device may be provided. The integrated sensordevice then comprises a semiconductor substrate, a light emitting unitformed into the semiconductor substrate, a light detecting unit formedinto the semiconductor substrate, and a waveguide formed into thesemiconductor substrate between the light emitting unit and the lightdetecting unit. The waveguide is formed in a portion of thesemiconductor substrate open to an environment to provide interactionbetween guided light and a measurement medium surrounding the waveguide.The light emitting unit is formed in a portion of the semiconductorsubstrate sealed off the environment. Further, the light emitting unitin the sealed portion is at least partially surrounded by an evacuatedcavity. The integrated sensor device may be used as NDIR CO₂ sensor, forexample.

To summarize, some embodiments combine an integrated infrared emitter, acollimation unit and a spectral filter on a single silicon element. Thiselement is thermally isolated from the surrounding material by evacuatedcavities. Some embodiments provide an infrared emitting unit that maydirectly couple the signal into a fiber element for immediateinteraction of IR signal and surrounding fluid. The usage of silicon asemitter and wave guide material may lead to a very compact integrationof collimator and filter elements. A sideways main propagation ofinfrared signals allows simple ways of integration of optical elements.The usage of a combined silicon-on-nothing and sealing techniqueguarantees minimum thermal losses by providing an evacuated cavitysurrounding the emitter element.

Various embodiments include:

-   -   Infrared emitting element with sideways signal outlet;    -   Element made from SON silicon with a filament that is surrounded        by beam shaping elements and filters, in the same level inside        the silicon construction;    -   Emitting unit that is surrounded by an evacuated cavity;    -   Emitting unit that couples the IR beam directly into a silicon        wave guide in the same level inside the silicon construction;    -   Wave guide element formed by means of SON and deep trench etch        processes, in one embodiment formed as a sub-wavelength        waveguide (concerning width and/or height).

The above shown examples may be configured with parts omitted, such asan emitting unit without a filter system. Further on, other elements maybe combined. One example would be a drain for unused spectral componentsattached to the emitting unit. Such a drain could be a filter systemthat has an inverted transmission functionality compared to the filtershown in FIG. 4. This second filter may be combined with the collimatorat defined regions. The emitting filament may also be formed in anon-cylindrical way (e.g. as a plate).

The description and drawings merely illustrate the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its spirit and scope. Furthermore,all examples recited herein are principally intended expressly to beonly for pedagogical purposes to aid the reader in understanding theprinciples of the disclosure and the concepts contributed by theinventor(s) to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass equivalents thereof.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example embodiment. While each claim may stand on its own as aseparate example embodiment, it is to be noted that—although a dependentclaim may refer in the claims to a specific combination with one or moreother claims—other example embodiments may also include a combination ofthe dependent claim with the subject matter of each other dependent orindependent claim. Such combinations are proposed herein unless it isstated that a specific combination is not intended. Furthermore, it isintended to include also features of a claim to any other independentclaim even if this claim is not directly made dependent to theindependent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or claims may not be construedas to be within the specific order. Therefore, the disclosure ofmultiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments a single act may include ormay be broken into multiple sub acts. Such sub acts may be included andpart of the disclosure of this single act unless explicitly excluded.

What is claimed is:
 1. An integrated light emitting device, comprising:a substrate of semiconductor material, wherein the substrate includes amain surface extending in a lateral direction; a light emitting unitintegrated into the semiconductor material of the substrate, wherein thesubstrate and light emitting unit are monolithically formed from thesemiconductor material; and at least one cavity formed into thesemiconductor material between the substrate and the light emittingunit, wherein the at least one cavity is configured to insulate thelight emitting unit and the substrate from each other.
 2. The integratedlight emitting device of claim 1, wherein the light emitting unitcomprises an electrically conductive structure formed vertically in thesemiconductor material as a light source, wherein the electricallyconductive structure is configured to emit light when a supply voltageis applied to terminals of the electrically conductive structure.
 3. Theintegrated light emitting device of claim 2, wherein the electricallyconductive structure comprises an electrically conductive filamentextending perpendicular to the lateral direction of the light beamemitted from the light emitting unit.
 4. The integrated light emittingdevice of claim 2, wherein the light emitting unit further comprises abeam shaping portion extending in the lateral direction and configuredto collimate light emitted from the electrically conductive structure.5. The integrated light emitting device of claim 4, wherein the beamshaping portion comprises a light-reflecting curved or parabolic edge ofa semiconductor material of the light emitting unit.
 6. The integratedlight emitting device of claim 5, wherein the electrically conductivestructure substantially extends through a focus of the light-reflectingcurved or parabolic edge.
 7. The integrated light emitting device ofclaim 1, wherein the light emitting unit is configured to emit a lightbeam directed in the lateral direction.
 8. The integrated light emittingdevice of claim 1, wherein the light emitting unit further comprises afilter portion formed in the semiconductor material.
 9. The integratedlight emitting device of claim 8, wherein the filter portion isconfigured to have at least one pass band in a spectral infrared region.10. The integrated light emitting device of claim 8, wherein the filterportion comprises one or more trenches formed into a semiconductormaterial of the light emitting unit.
 11. The integrated light emittingdevice of claim 1, wherein the light emitting unit is arranged in aportion of the semiconductor material sealed off from an environment,and wherein the light emitting unit in the sealed portion is at leastpartially surrounded by an evacuated cavity.
 12. The integrated lightemitting device of claim 1, further comprising: at least one insulatingsupport structure coupled between the light emitting unit and thesubstrate, wherein the at least one cavity and the at least oneinsulating support structure are configured to insulate the lightemitting unit and the substrate from each other.
 13. The integratedlight emitting device of claim 1, further comprising: a sealing layerformed above the light emitting unit; and at least one cavity betweenthe light emitting unit and the sealing layer.
 14. The integrated lightemitting device of claim 1, further comprising: a waveguide coupled to alight outlet of the light emitting unit, wherein the waveguide isconfigured to provide interaction between guided light and a measurementmedium surrounding the waveguide.
 15. The integrated light emittingdevice of claim 14, wherein the waveguide and the light emitting unitare integrally formed into the semiconductor material, wherein thewaveguide and light emitting unit are monolithically formed from thesemiconductor material.
 16. An integrated sensor device, comprising: asemiconductor substrate, wherein the semiconductor substrate includes amain surface extending in a lateral direction; a light emitting unitformed into the semiconductor substrate, wherein the semiconductorsubstrate and light emitting unit are monolithically formed from asemiconductor material; a light detecting unit formed into thesemiconductor substrate; and a waveguide formed into the semiconductorsubstrate between the light emitting unit and the light detecting unit;wherein the waveguide is formed in a portion of the semiconductorsubstrate open to an environment to provide interaction between guidedlight and a measurement medium surrounding the waveguide, wherein thelight emitting unit is formed in a portion of the semiconductorsubstrate sealed off from the environment, and wherein the lightemitting unit in the sealed portion is at least partially surrounded byan evacuated cavity such that the light emitting unit and thesemiconductor substrate are insulated from each other.
 17. Theintegrated sensor device of claim 16, wherein the light emitting unit isconfigured to emit a light beam in the lateral direction.
 18. Theintegrated sensor device of claim 16, further comprising at least oneinsulating support structure coupled between the light emitting unit andthe semiconductor substrate.
 19. A method for forming an integratedlight emitting device, the method comprising: integrating a lightemitting unit into a semiconductor material of a semiconductorsubstrate, wherein the semiconductor substrate and light emitting unitare monolithically formed from the semiconductor material; and formingat least one cavity into the semiconductor material between thesemiconductor substrate and the light emitting unit.
 20. The method ofclaim 19, further comprising: depositing at least one insulating supportstructure on semiconductor substrate such that the at least oneinsulating support structure is coupled between the light emitting unitand the semiconductor substrate.